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13 C NMR investigation of the reaction in water of UF resins with blocked emulsifiable isocyanates

2005; Wiley; Volume: 99; Issue: 2 Linguagem: Inglês

10.1002/app.22498

1097-4628

A. Despres, A. Pizzi, L. Delmotte,

Dental materials and restorations

Abstract A solid state 13 C NMR study of hardened networks obtained by the reaction of blocked and nonblocked isocyanates (pMDI) with urea‐formaldehyde (UF) resins in water showed different results according to the temperature of the reaction. At high temperature, in water, both a nonblocked or an emulsifiable, blocked isocyanate, appear to crosslink with UF resins through the formation both of traditional methylene bridges connecting urea to urea and of urethane bridges. The latter have been confirmed by 13 C NMR to form in water by reaction of the isocyanate NCO group with the hydroxymethyl groups of the UF resin. At ambient temperature, UF/pMDI resins where the pMDI is a emulsifiable blocked isocyanate, do not appear to form urethanes to any great extent but rather to crosslink through the usual UF resin urea to urea methylene bridges. Even in this case, when urethane bridges appear to be absent, evidence of crosslinking in water through reaction of the isocyanate with the NH 2 and NH amide of the UF resin has not been observed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 589–596, 2006